(a) Field of the Invention
This invention relates to a control system for an in-cylinder direct injection engine which controls behavior of fuel spray, directly injected into a combustion chamber in a cylinder, with a tumble to combust a mixture stratified around an electrode of a spark plug, and more particularly relates to the technical field of compensation control for suppressing deterioration in combustion quality of the mixture resulting from individual differences between injectors.
(b) Description of the Prior Art
Conventionally, control systems for in-cylinder direct injection engines of this type include one which is adapted to control penetration of fuel spray from an injector in accordance with the intensity of a tumble, carry the fuel spray toward a spark plug by means of the tumble and stratify a mixture around an electrode of the spark plug, as disclosed in, for example, Japanese Unexamined Patent publication No. 2000-204954.
Specifically, in the above control system, a tumble control valve (TCV) is provided in an intake passage of the engine downstream of a throttle valve. The TCV is opened or closed by an actuator to control the intensity of the tumble in the combustion chamber. At the same time, the fuel injection pressure of the injector is correspondingly controlled so that the fuel spray penetration is balanced against the tumble. In this manner, the fuel spray from the injector is carried by means of the tumble to reach the vicinity of the electrode of the spark plug, which enables stable stratified combustion.
However, for in-cylinder direct injection engines in which a fuel is injected directly into the high-pressure combustion chamber, their injectors generally have much higher fuel injection pressures as compared with those of injectors included in so-called port injection engines, and therefore the injectors are likely to have large variations in fuel injection pressure due to their individual differences.
Further, for multi-cylinder engines such as the above-mentioned prior art (Japanese Unexamined Patent Publication No. 2000-204954), a plurality of cylinders included in a single engine have individual intake ports of slightly different shapes and therefore the combustion chambers in the cylinders are not necessarily equal to each other in tumble intensity.
Accordingly, even if the fuel injection pressures of the injectors are commonly controlled in order to change in accordance with the tumble in the above-mentioned manner, balance is not strictly offered of the fuel spray penetration and the tumble in each cylinder. This results in the inconvenience that the mixture around the spark plug is held against stratification and thereby degrades its ignitability and combustion quality.
In addition, for the multi-cylinder engines such as the prior art, the degree of unbalance of fuel spray penetration and tumble is different from cylinder to cylinder. This also incurs another problem of increasing variations in combustion from cylinder to cylinder and in particular increasing noises and vibrations (idling vibrations) due to torque variations caused during idling operation and the like.
The present invention has been made in view of the forgoing problems, and therefore its object is to provide a control system for an in-cylinder direct injection engine which enables suitable mixture stratification by controlling behavior of fuel spray by means of a tumble, and particularly to provide suitable mixture stratification by considering a deviation of fuel injection pressure of a fuel from each injector and eliminating the unbalance of fuel spray and tumble which results from the deviation.
To attain the above object, in the present invention, the fuel injection pressure of a fuel injection valve is intentionally decreased or increased so that the unbalance of fuel spray and tumble is clarified, and a fuel injection timing is compensated so that even in such a condition combustion variations of an engine can fall within an allowable range.
Specifically, as shown as an example in FIG. 1, a first aspect of the invention has as a precondition a control system A for an in-cylinder direct injection engine which includes: a fuel injection valve 18 for directly injecting a fuel into a combustion chamber 6 in a cylinder 2 of an engine 1; and a tumble generating means 10 for generating a tumble in the combustion chamber 6, in which the fuel is injected against the tumble in the combustion chamber 6 by the fuel injection valve 18 during stratified-charge combustion operation of the engine 1 so that a flammable mixture stays in the vicinity of an electrode of a spark plug 16 at the ignition timing for the cylinder 2.
Also, the control system A further includes: a fuel pressure control means 200 for controlling the fuel injection pressure of the fuel injection valve 18; a fuel pressure forcibly changing means 50b for forcibly changing the fuel injection pressure to be controlled by the fuel pressure control means 200 from a reference injection pressure corresponding to operating conditions of the engine 1; a combustion variation detecting means 50c for detecting the degree of combustion variation in the engine 1 when the fuel injection pressure has been changed by the fuel pressure forcibly changing means 50b; and an injection timing compensation means 50e for compensating the fuel injection timing of the fuel injection valve 18 so that the degree of combustion variation in the engine 1 detected by the combustion variation detecting means 50c becomes smaller than that in a preset reference condition.
First, according to part of the control system A which constitutes the precondition, the fuel is injected from the fuel injection valve 18 against a tumble generated by the tumble generating means 10 during stratified-charge combustion operation of the engine 1, and the fuel spray is reduced in speed by the tumble and thereby stratified around the electrode of the spark plug 16. In this case, if the fuel injection valves 18 have deviated fuel injection pressures due to their individual specificities, it can be expected that the fuel spray penetration is relatively weak so that the mixture may not sufficiently reach the vicinity of the spark plug 16 electrode or that contrarily the fuel spray penetration is relatively intense so that the mixture may pass over the vicinity of the spark plug 16 electrode whereby ignitability and combustion quality may be impaired.
On the other hand, according to the above-mentioned characteristic structure of the control system A, the fuel injection pressure of the fuel injection valve 18 is first changed forcibly by the fuel pressure forcibly changing means 50b, so that the deviation of penetration of fuel spray from the fuel injection valve 18 is amplified. This deteriorates ignitability and combustion quality of the mixture so that an increased degree of combustion variation of the engine 1 will be detected by the combustion variation detecting means 50c. Also, the fuel injection timing is compensated by the injection timing compensation means 50e such that even in that condition the degree of combustion variation of the engine 1 becomes smaller than that in the reference condition. In other words, for example, if the spray penetration is relatively weak, advancing the fuel injection timing allows the mixture to reach the vicinity of the spark plug 16 electrode at a suitable timing. On the other hand, if the spray penetration is relatively intense, a retarded fuel injection caused by retarding the injection timing allows the mixture to reach the vicinity of the spark plug 16 electrode at a suitable timing.
In short, according to the present invention, the unbalance of fuel spray and tumble can be eliminated by compensation for the fuel injection timing, thereby providing suitable mixture stratification. This enhances ignitability and combustion quality of the mixture thereby providing further improved fuel economy and power output performance.
In a second aspect of the invention, the control system includes a combustion variation determining means (50d) for comparing the degree of combustion variation of the engine (1) detected by the combustion variation detecting means (50c) with that in the reference condition to determine that the detected degree of combustion variation is larger than that in the reference condition, and the injection timing compensation means (50e) is adapted to compensate the fuel injection timing when the combustion variation determining means (50d) determines that the detected degree of combustion variation is larger than that in the reference condition.
With this arrangement, when the combustion variation determining means (50d) determines that the detected degree of combustion variation of the engine (1) is larger than that in the reference condition, compensation for the fuel injection timing by the injection timing compensation means (50e) provides stable mixture stratification thereby ensuring the ignitability and combustion quality of the mixture. On the other hand, if the detected degree of combustion variation is smaller than that in the reference condition, the mixture has sufficient ignitability and therefore, in this case, the injection timing will not be compensated.
In a third aspect of the invention, the engine (1) is a multi-cylinder engine having a plurality of cylinders (2), and the injection timing compensation means (50e) is adapted to compensate the fuel injection timing for each cylinder (2) of the engine (1).
Generally, in the multi-cylinder engine (1), if combustion variations between the cylinders are increased due to the unbalance of fuel spray and tumble in each cylinder (2), so-called idling vibrations may be increased so as to give the driver an uncomfortable feeling. Effects of this aspect of the invention, however, are particularly effective to such a problem.
In a fourth aspect of the invention, the fuel pressure forcibly changing means (50b) in the second aspect effects a pressure reductively changing control of changing the fuel injection pressure of the fuel injection valve (18) so that the fuel injection pressure becomes lower than a reference injection pressure and a pressure augmentatively changing control of changing the fuel injection pressure so that the fuel injection pressure becomes higher than the reference injection pressure, and the injection timing compensation means (50e) compensates the fuel injection timing of the fuel injection valve (18) to the advance side if the degree of combustion variation of the engine (1) has become larger than that in the reference condition as the result of a pressure reductively changing control of the fuel pressure forcibly changing means (50b) while compensating the fuel injection timing to the retard side if the degree of combustion variation of the engine (1) becomes larger than that in the reference condition as the result of a pressure augmentatively changing control of the fuel pressure forcibly changing means (50b).
In this case, if the fuel pressure forcibly changing means (50b) effects a pressure reductively changing control to reduce fuel spray penetration so that the degree of combustion variation of the engine (1) becomes larger, this means that the fuel spray penetration is originally deviated on a relatively weak side. Accordingly, in this case, the fuel injection timing of the fuel injection valve (18) is compensated to the advance side by the injection timing compensation means (50e), and the unbalance of fuel spray penetration and tumble can be thereby eliminated. On the contrary, if the fuel pressure forcibly changing means (50b) effects a pressure augmentatively changing control to increase fuel spray penetration so that the degree of combustion variation of the engine (1) becomes larger, this means that the fuel spray penetration is originally deviated on a relatively intense side. In this case, the fuel injection timing will be compensated to the retard side.
In a fifth aspect of the invention, the fuel pressure forcibly changing means (50b) in the fourth aspect is arranged to effect a pressure reductively changing control to gradually reduce the fuel injection pressure of the fuel injection valve (18) to a predetermined lower limit and effect a pressure augumentatively changing control to gradually increase the fuel injection pressure to a predetermined upper limit.
With this arrangement, the fuel pressure forcibly changing means (50b) first gradually changes the fuel injection pressure of the fuel injection valve (18) to the predetermined upper or lower limit, and the injection timing compensation means (50e) then effects compensation control so that even in either of the above two conditions of the fuel injection pressure the degree of combustion variation of the engine (1) becomes smaller than that in the reference condition. As a result, the unbalance of fuel spray penetration and tumble can be eliminated. In addition, in that case, since the fuel injection pressure of the fuel injection valve (18) is gradually changed to the predetermined upper or lower limit and the injection timing is gradually compensated by the injection timing compensation means (50e) in correspondence with the change of the injection pressure, it can be prevented that during the time an excessive combustion variation or a misfire occurs.
In a sixth aspect of the invention, when the combustion variation determining means (50d) determines that the detected degree of combustion variation of the engine (1) is smaller than that in the reference condition after the fuel pressure forcibly changing means (50b) in the fifth aspect has effected either one of the pressure reductively changing control and pressure augumentatively changing control, the fuel pressure forcibly changing means (50b) effects the other.
In this manner, the fuel injection pressure of the fuel injection valve (18) is first gradually changed to one of the predetermined lower and upper limits, it is confirmed in that state that the degree of combustion variation of the engine (1) is sufficiently small, the fuel injection pressure is then gradually changed to the other limit, and it is also confirmed in that state that the degree of combustion change of the engine (1) is sufficiently small. As a result, whether the fuel spray penetration for each cylinder (2) is deviated on a weak side or intense side relative to the tumble, the unbalance of them can be eliminated.
In a seventh aspect of the invention, the fuel pressure forcibly changing means (50b) and the injection timing compensation means (50e) are arranged to effect the changing of the fuel injection pressure of the fuel injection valve (18) and the compensation for the fuel injection timing, respectively, in idling operating conditions of the engine (1).
In this manner, in the idling operating conditions of the engine (1), the degree of combustion variation of the engine (1) can be accurately detected by excluding the effects of angular variations in a vehicle power transmission system and vibrations from a road surface. In addition, in the idling operation, the fuel injection timing is compensated so that combustion variations from cylinder to cylinder can be reduced, which prevents the occurrence of an uncomfortable idling vibration.
In an eighth aspect of the invention, the control system further includes an injection timing control means (50a) for controlling the fuel injection timing of the fuel injection valve (18) in accordance with operating conditions of the engine (1), and a learning control means (50f) for obtaining a learning value based on a compensated amount of the fuel injection timing by the injection timing compensation means (50e) and reflecting the learning value on the control of the injection timing control means (50a) over the fuel injection timing.
With this structure, the learning value for the compensation of the injection timing is obtained by the learning control means (50f) based on the compensated amount of the fuel injection timing by the injection timing compensation means (50e), and the learning value is reflected on the control of the injection timing control means (50a) over the reference fuel injection timing. This eliminates, in a relatively short learning time, deterioration of ignitability and combustion quality which will be induced due to deviations of the fuel spray penetration or the like in the entire stratified-charge combustion zone of the engine (1), thereby providing further improved fuel economy and power output performance of the engine (1).
In a ninth aspect of the invention, an in-cylinder direct injection engine system includes: a fuel injection valve for directly injecting a fuel into a combustion chamber in a cylinder of an engine; an intake port capable of generating a tumble in the combustion chamber; a regulator for regulating the fuel pressure of the fuel to be supplied to the fuel injection valve; a revolving speed sensor for detecting the revolving speed of the engine; a crank angle sensor for detecting the rotational angle of a crank shaft; a fuel pressure sensor for detecting the pressure of the fuel being supplied to the fuel injection valve; and a control unit for controlling the fuel injection timing and fuel pressure of the fuel injection valve based on a signal from at least one of the revolving speed sensor, the crank angle sensor and the fuel pressure sensor.
Further, the control unit is adapted to set based on at least the engine revolving speed a reference target value for control on the fuel pressure to be regulated by the regulator, set based on at least the engine revolving speed a reference target value for control on the fuel injection timing of the fuel injection valve, change the setting of the reference target value for control on the fuel pressure to increase or decrease the target value followed by controlling the regulator so that the value detected by the fuel pressure sensor reaches the changed target value, retard the fuel injection timing of the fuel injection valve behind the reference target value for control on the fuel injection timing if the rate of change of values detected by the crank angle sensor becomes larger than a preset reference value as the result of an augmentative setting of the target value for control on the fuel pressure, and advance the fuel injection timing of the fuel injection valve ahead of the reference target value for control on the fuel injection timing if the rate of change of values detected by the crank angle sensor becomes larger than the preset reference value as the result of a reductive setting of the target value for control on the fuel pressure.
With this structure, the same operations and effects as in the first, second and fourth aspects are exhibited.
As described so far, according to the first aspect of the invention, in the in-cylinder direct injection engine in which a tumble is generated in the combustion chamber of the cylinder during stratified-charge combustion operation of the engine and a fuel is injected against the tumble by the fuel injection valve so that a flammable mixture which stays in the vicinity of the spark plug electrode is ignited at the ignition timing of the cylinder, the unbalance of fuel spray and tumble can be eliminated by compensation for the fuel injection timing thereby providing suitable mixture stratification. This enhances ignitability and combustion quality of the mixture thereby providing further improved fuel economy and power output performance.
According to the second aspect of the invention, since there is provided a combustion variation determining means for comparing the degree of combustion variation of the engine detected by the combustion variation detecting means with that in the reference condition, compensation for the fuel injection timing can be further reliably effected by the injection timing compensation means when the detected degree of combustion variation is large, thereby providing stable mixture stratification.
According to the third aspect of the invention, in the multi-cylinder engine, the unbalance of fuel spray versus tumble can be eliminated so that combustion variations from cylinder to cylinder can be largely reduced, which prevents the occurrence of an uncomfortable idling vibration.
According to the fourth aspect of the invention, when the fuel injection pressure of the fuel injection valve is reduced, the unbalance of fuel spray penetration and tumble can be eliminated by compensating the fuel injection timing to the advance side through the injection timing compensation means, and when the fuel injection pressure is increased, the unbalance can be eliminated by compensating the fuel injection timing to the retard side.
According to the fifth aspect of the invention, since the fuel injection pressure of the fuel injection valve is gradually changed to the predetermined lower or upper limit, the unbalance of fuel spray penetration and tumble can be eliminated without any excessive combustion variation and misfire during the time.
According to the sixth aspect of the invention, the fuel injection pressure of the fuel injection valve is continuously changed between the predetermined lower and upper limits and the fuel injection timing is compensated correspondingly. As a result, whether the fuel spray penetration is deviated on a weak side or intense side relative to the tumble, the unbalance of them can be eliminated.
According to the seventh aspect of the invention, since the changing of the fuel injection pressure and the compensation for the fuel injection timing of the fuel injection valve are effected in idling operating conditions of the engine, this enables accurate detection of the degree of combustion variation of the engine and prevention of the occurrence of an uncomfortable idling vibration.
According to the eighth aspect of the invention, a learning value is obtained based on a compensated amount of the fuel injection timing and reflected on the control over the reference fuel injection timing, which eliminates deterioration of ignitability and combustion quality which will be induced due to deviations of fuel spray penetration or the like in the entire stratified-charge combustion zone of the engine and thereby provides further improved fuel economy and power output performance of the engine.
According to the ninth aspect of the invention, the same effects as in the fourth aspect can be obtained.